1. Field of the Invention
This invention relates to sheet feeding devices for printing apparatus and more particularly to a sheet feeding device for a printing apparatus which enables skewless sheet feeding to be effected automatically.
2. Description of the Prior Art
In printing apparatus such as typewriters and printers, it is necessary that each sheet which is fed to a platen or to a printing station by the platen be fed straight and have no skew. The usual practice is that a pressing roller maintained in pressing engagement with the platen is released from engagement therewith and a sheet has its position corrected manually if it has a skew.
In recent years, popularization of automation in document production has made it necessary to effect sheet feeding automatically. However, realization of full benefits from automatic sheet feeding has been hampered by the need to correct the position of a sheet manually if the sheet is at an angle.
An increase in the speed at which a printing apparatus is operated has rendered loss of the time which is required for correcting the position of a sheet when it has a skew unacceptable. Proposals have been made to use a method in which the leading edge of a sheet is caused to impinge against the contacting portions of a platen and a pressing roller in pressing engagement with each other, as a means for automatically preventing the skewing of the sheet.
A skew generally occurs in a sheet when it is caught in the nip between the pressing roller and the platen. A skew is produced in a sheet largely because it is difficult to cause the entire leading edge portion of a sheet to be caught at one time time by the platen and pressing roller due to the fact that a slip tends to occur between the sheet and the platen. Thus the method of the prior art in which the leading edge of a sheet is caused to impinge against the contacting portions of the platen and pressing roller is not capable of effectively preventing the skewing of a sheet.